Print hammer unit for high speed printers



DCC. 26, 1967 s. ARNOLD ETAL 3,359,921

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS Filed Juiy 19, 1965 s sheeheet1 -f N I cq Ln n' CC N l INVENTORS SIEGHARD ARNOLD GEROLD BUHRMANNJURGEN HAASIS HORST HEINRICH MANFRED NITSCHKE GUNTHER SCHACHT EBERHARDSPIETH f BYQAWM@ ATTORNEY Dec. 26, 1967 Filed July 19, 1965 1s.' ARNOLDETAL 3,359,921

PRINT HAMMER UNIT FOR HIGH SPEED PRINTERS 8 Sheets-Sheet 2 FIG. 3

FIG.2

Dec. 26, 1967 Filed July 19, 1965 S. ARNOLD ETAL PRINT HAMMER UNIT FORHIGH SPEED PRINTERS 8 Sheets-Sheet 5 FIG.5

FIG. 4

Dec 26, 1967 E s. ARNOLD ETAL. 3,359,921

PRINT HAMMER UNI'KIl FOR HIGH SPEED PRINTERS FiledJuly 19,` 1965ssheetS-sheet 4 Dec. 26, 1967 s. ARNOLD ETAL PRINT HAMMER UN'IT FOR HIGHSPEED PRINTERS 8 Sheets-Sheet v5 Filed July 19, 1965 HG. au

FIG.8

, FIG.7

Dec. 26, 1967 s. ARNOLD ETAL PRINT HAMMER UNIT FOR HIGH SPEED PRINTERSFiled July 19, 1965 B-Shets-Sheet 7 l FIG. 1o

De@ 26,1967 s. ARNOLD ETAL PRINT HAMMER UNIT FOR HIGH SPEED PRINTERSFiled July 19, 1965 8 Sheets-Sheet 8 HAMMER FLIGHT TIME VS. BUCK OFF NIFIG. v12| 4176 92 zlo HAMMER FLIGHT .TIME VS. VOLTAGE FIG. 172e (psec)HAMMER FLIGHT TIMEJ HAMMER FLIGHT TIME/ 15% (vous) I l VOLTAGE FOROHOLDANO BUCK OFF WINDING United States Patent O 3,359,921 PRINT HAMMER UNITFOR HIGH SPEED PRINTERS Sieghard Arnold, Hildrizhausen-Boblingen, GeroldBhrmann, Stuttgart, Jrgen Hansis, Boblingen, Horst Heinrich,Stuttgart-Bad Cannstatt, Manfred Nitschke, Stuttgart-Rohr, GnterSchacht, Boblingen, and Eberhard Spieth, Holzgerlingen, Germany,assignors to International Business Machines Corporation, Armonk, N.Y.,a corporation of New York Filed July 19, 1965, Ser. No. 473,093 Claimspriority, application Germany, .luly Z5, 1964,

J 26,273 14 Claims. (Cl. lill-93) ABSTRACT F THE DISCLOSURE Printingapparatus for a high speed printer having an elongated print hammerIwith an upstanding armature portion at the end remote from the printline and a pair of parallel flat springs supporting the print hammer. Anelectromagnet having a hold winding for producing magnetic flux to holdthe print hammer in a retracted position and means for reducing themagnetic flux below the holding value to permit the support springs toactuate the hammer to a printing position.

This invention relates to a print hammer unit, and in particular to aprint hammer unit for a high speed printer which is used as an outputdevice for an electronic data processing machine.

Generally, modern high speed printers of this type work in such a mannerthat a type carrier is provided which contains several sets of allcharacters to be printed, and which carries out a periodic movement sothat each printable character is oiered to each print position of aprint line. A rotating type drum, a type chain moving in the print linedirection or a type bar moving back and forth periodically in the printline direction can be used as a type carrier. At each print position ofa print line a print hammer is provided which is released at a suitablemoment, i.e., ywhen the type to be printed is in the corresponding printposition. For the control of the print hammer impact an electronicrepresentation is formed of the print type which is in an individualprint positions each time, with reference to a certain position of thetype carrier. In a so-called scan, in passing from print position toprint position, this electronic representation is compared with the textof a print line which is also stored electronically in a data processingmachine, If the two coincide for any print position, the print hammercorresponding to this print position is released.

A particularly difficult problem connected with such high speed printersoccurs in the print hammer mechanism. On the one hand, it is verydifficult to make the individual print hammers and their drives of suchan extreme tlatness that they do not take up more space than the Widthof a print character, and to arrange all the print hammers closelypacked in a row of approximately 130 print positions forming the printline, and to also provide for adjustment thereof. On the other hand, theprint hammers should have a considerable but clearly defined amount ofkinetic energy in order to obtain a uniform print on several copies, andthe hammer motion, with the hammer ilight time of some millisecondsduration, has to be exactly reproducible. As in general such printersfollow the principle of on-the-fly impact, that is, as the type carrieris not stopped by the hammer impact, the contact of the print hammerwith the type flying by must be of very short duration.

A well known print hammer mechanism for such high lCC speed printersworks in such a manner that the armature and electromagnet acceleratethe print hammer. As the magnet only fires the print hammer, which thenmoves on in free flight, a great number of factors have to be taken intoconsideration with regard to the hammer motion, and an exactlyreproducible hammer motion can be obtained only with great diiculty.

In another well known print hammer mechanism rotational kinetic energyis transferred through a cam or through a pushing process onto the printhammer. In that application the electromagnet only effects the releaseof the print hammer at a predetermined moment, but as the print hammerenergy is taken from a continuously rotating drive, it is possi-ble toobtain a greater eXactness in the hammer motion. Such a mechanism,however, presents considerable construction difficulties, in particularon account of the high mechanical stress on the parts participating inthe push process at increased speeds. The inertia of the controlelements is another factor impeding an increase in speed with this typeof mechanism.

In another print hammer mechanism known t0 the art, potential energystored in a spring is used for the print hammer drive. In that systemthe print hammer is shiftably arranged in a guide, and a stretchedspring is gripped yby a latch. Here too, the release takes place througha control mechanism operated by an electromagnet.

In order to avoid the disadvantages connected with the use of mechanicalcontrol parts, and to reduce the inertia in the control of the printhammer release, it is also known to hold the print hammer against theforce of a stretched spring through the use of a magnet, and tode-excite the magnet to obtain the print hammer release. In a Well knownprint hammer unit of that kind the print hammer is supported suitablyVon an axle and is designed as a t-Woarmed lever, the one lever arm ofwhich serves as an armature, whereas the actuating spring engages theother lever arm. This print hammer mechanism, however, has as lone ofits disadvantages the fact that the support of the print ham-mer on anaxle requires an uncomfortably large Width for the hammer drives.Through this support, friction losses are caused, which consume part ofthe hammer energy. Besides it is quite diflicult to adjust all printhammers in such a manner that they t against the various magnets withoutair gaps, which is a condition absolutely necessary for obtaining anaccurately defined hammer motion. Fnally, the magnet windings have to behoused in a very narrow 4winding space. This limits the power of theholding magnets, which in turn puts a limit on the strength of thedriving spring. Furthermore, this print hammer unit is complicated inits construction and requires a large amount of maintenance.

This invention, the aim of which is to provide a print hammer unitworking quickly and exactly, and lwhich does not take up much space andoperates very safely, in addition to using a minimum of Wearable partsrequiring maintenance, relates to a print hammer unit where potentialenergy which has been stored in a spring is used for print hammeractuation, and where the print hammer release is effected throughdeactivation of the magnet holding the tensioned print hammer.

In order to avoid the aforementioned disadvantages, the print hammerunit of the present invention is of such a design that potential energyis stored in elastic elements, preferably flat springs, which arerelatively rigid to tensile and torsional stress, and are subjected tobending only, and which at the same time provide supports for the printhammer, and are arranged in such a manner that the print hammer motionconsists of a parallel movement.

Using this principle, a printing unit as disclosed by this invention isadvantageously constructed in such a manner that the print hammers areformed as flat rods having a bent portion serving as an armature. Saidrods form components of an operational atness which can be replacedindividually, along with their supports which consist of two fiatsprings arranged vertically and fixed in a foot plate.

More advantages of the print hammer unit as disclosed by this inventionare that the tensioned print hammers associated with the individualprint positions are held by means of electromagnets consisting of amagnet yoke arranged at each print position and a magnet winding commonto all the magnet yokes, and that for the deactivation of theelectromagnets holding the tensioned print hammers, release windings arearranged at the individual print positions on the magnet yokes in such amanner that the magnetic field each produces compensates or neutralizesthe field of the holding magnet, or removes it from the armature,respectively.

In order to obtain a very short and well defined release time of thearmature at the print hammer release, the print hammer unit as disclosedby the invention is of such a design that the magnetic field of theholding magnet is overcompensated for, through the magnetic field of thereleasing magnet at the print position in question. Furthermore, thepresent invention provides for the holding winding, which iscontinuously energized and which is common to all magnet yokes, to beconnected in series with an inductance of a high v-alue in order toavoid the iniiuences of changes of the magnetizing force at theindividual magnet yokes on the holding liux.

For obtaining a holding force independent of voltage variations it isadvantageous that the magnet yokes near their pole faces have a crosssection which is reduced in comparison with the cross section of theremainder of the magnetic circuit, so that in that area they aremagnetized to the saturation point.

An important advantage of the print hammer unit as disclosed in thepresent invention is that the magnet yokes, preferably in pairs, aresecured by means of tensioned clamps to bars mounted on a support. Ithas been found to be desirable to have impressed in the faces of the barsurfaces and the inner jaws of the tensioned clamps pressing the magnetyokes against the bars, respectively, hard crystals such as sinteredA1203 (corundu-m). This has the effect that the magnet yokes are soaligned individually against their print hammers that upon excitation ofthe mold magnets, and when their respective clamps have been released-by a key, they locate themselves against the corresponding magnetarmature without an air gap being formed. It is thus possible to adjustall magnet yokes within the shortest time through a simple manipulationwithout the risk of twisting or overtensioning of the support holdingthe magnet yokes.

The print hammer unit disclosed by the invention is of such structurethat the magnet yoke support is equally supported on leaf springs whichare arranged in such a manner that it can be shifted with a parallelmotion, and then it carries out a movement of going periodically backand forth and being directed in a vertical direction rela-l tive to theplaten which serves for the return of the fired print hammers. Suchmovement is preferably effected by means of a cam gear.

An uncomplicated and safe method of securing and adjusting theindividual print hammer units is obtained in the printing device asdisclosed yby the invention, by securing the print hammer units,preferably in pairs, by means of foot plates to stationary guidingplates so that the print hammer units can be shifted or adjustedindividually.

In order to guarantee uniform connections at the clamping points of theleaf springs carrying the print hammers, the leaf spring structures aredesigned in such a manner that the springs carrying the print hammersare surrounded at their tops and bottoms with coatings of an elasticsubstance which fills cavities in the print hammers and the foot platesin which the spring ends are welded, said coatings being tapered towardsthe middle of the springs.

Another advantage of the print hammer unit as disclosed by thisinvention is that spring U-bolts are provided which slide in thedirection of the leaf springs carrying the print hammers, and whichfurthermore t against the leaf springs at their ends, and which arecombined structurally to be slidably supported in the foot plate of thecorresponding print hammer unit. These U-bolts serve for adjusting thehammer flight time. rIhrough a small shifting of these U-bolts themanufacturing tolerances in the thickness of the leaf springs carryingthe print hammers can be compensated for.

Finally the print hammer unit of this invention is characterized in thatat the individual print positions elastically fixed damping material isprovided which absorbs the energy of the print hammers moving back afterthe print impact, and which by means of elastic stops, locks the printhammers until the magnet yokes, when moved to their extreme forwardpositions, have magnetically attracted their respective hammers. In anadvantageous manner the damping material is arranged on a supportextending over all of the print positions, which support is pivotallymounted and offset from the elastic stops in a downward direction, bymeans of an axle. This support is pivotally movable for a short time torelease the print hammers, preferably by means of a cam gear.

The foregoing and other objects, features and advantages of the.invention will be apparent from the following more particulardescription of a preferred ernbodiment of the invention, as illustratedin the accompanying drawings.

In the drawings:

FIG. l is a partly broken away perspective drawing of a print hammerunit embodying the invention in one of its forms;

FIG. 2 is a schematic partly sectional view of the drive of a printhammer unit in side elevation and in the rest position;

FIG. 3 is the same view as shown in FIG. 2 but at the beginning of therestore motion of the print hammer;

FIG. 4 is the same view as shown in FIG. 2 but with the print hammersprings tensioned;

FIG. 5 is the same view as shown in FIG. 2 in an intermediate positionshortly after a print hammer impact;

FIG. 6 is an enlarged view of the holding magnets and their supportmeans;

FIG. 7 is a plan view of the holding magnets with their supportingclamps;

FIGS. 8a and 8b are top and side views respectively of the key used foradjusting the holding magnets and opening the support clamps;

FIG. 9 is an enlarged perspective view of the dampers at the moment ofbecoming effective upon the restore of the print hammers;

FIG. l0 is an enlarged side view of a print hammer and its support;

FIG. 11 is a sectional view along the line 11-11 of FIG. 10 showing moreclearly the securing of the leaf springs at their clamping points;

FIG. 12a.' is a schematic diagram of the circuits for the holdingmagnets together with the bucking windings therefor; and

FIGS. 12b and 12C show curves illustrating the hammer flight time v.bucking ampere turns and voltage, respectively.

In the printing unit shown in FIG. l a type bar 1 is used as a typecarrier which can be shifted longitudinally in a print line directionand which is designed in a comblike form. The type bar 1 is secured to atube 2 which moves in a guide 3. The type bar 1 is equipped with elastictongues 4 to whose free end the print types 5 are fixed. The spacing ofthe individual tongues corresponds with the spacing of the printpositions of the print line. During printing the print types 5 are movedagainst a paper sheet 7 placed over a platen 6. Ribbon 8 is guided overthe paper sheet 7. A stop bar 10 inserted in the guide block 9, in whichthe guide 3 is formed in part, limits the forward movement Iof theelastic tongues 4.

At each print position a print hammer 11 is provided which at a suitablemoment, i.e., when through shifting of the type bar 1, the type to beprinted is in the corresponding print position, strikes against the headof the elastic tongue 4 and thus elfects the printing of thecorresponding type. The print hammers 11 are secured at the heads of twoleaf springs 12, 13 which in turn are clamped at their foot end in afoot plate 14. The hardness of the leaf springs 12, 13 is selected insuch a manner that the springs are to be regarded as rigid with respectto pressure, tension, and torsion. They are only exposed to a bendingaction. Thus the movement of the print hammer secured to said springsprincipally consists of a parallel motion.

The print hammers, which may be considered as formed of little rodsconsisting of one piece, and are normally held in a tensioned statethrough a holding magnet. For that purpose they are L-shaped and have abent projection 15 which serves as a magnetic armature (FIG. 6). Witheach armature 15 a magnet yoke 16 is associated which is H-shaped. Polefaces 17, 18 lie at the ends of the free legs 19, 20 of the yoke 16opposite the armature 15. A magnet winding 21 extends over all themagnet yokes 16 and is housed in the cavity in the legs 19, 20 andcontinuously carries current during operation, so that the holdingmagnets for the individual print hammers are continuously excited. Legs19, 20 of the magnet yokes 16 have ledges 22, 23 near the pole faces atwhich the cross section -of the yokes is reduced. It thereby resultsthat the magnet yoke 16 within the area of their pole faces 17, 18 aremagnetized to the saturation point, and thus the holding force of theholding magnets is independent of voltage variations. In addition, theholding winding 21 is connected in series with an inductance device L ofa relatively high value (FIG. 12a) in order to avoid the effects ofvariations in the magnetizing force of the holding circuit during thefiring of the print hammers.

For the controllable release of the tensioned print hammers held by thehold magnets 16, windings 24, 25 are arranged -on the free legs 19, 20lof the magnet yokes 16, the magnetic field of which is formed uponapplying an electric pulse, being in an opposite direction to the lieldof the hold magnet at the respective print position. The windings 24, 25are of low inductance and the ampere turn value is regulated in such amanner that the magnetic eld of the holding magnet is not onlyneutralized or compensated for through the release of bucking windings24, 25 but is overcompensated for. Thus the crossover of the resultingmagnetic eld comes into the range of the rapidly increasing eld of thecompensating windings, and a very short and exactly reproducible releaseor dropping time of the print hammers is obtained. The compensatingwindings 24, 25 are arranged by means of the insulation support sleeves26, 27 on the legs 19, 20 of the magnet yokes 16, without the use of theusual spools. They are connected in series and have their connectionsmade t an insulating plate 30 mounted Ion the magnet yoke through rivets28, 29, and upon which plate they are soldered to a printed circuit 31.The lines of the printed circuit are in turn connected to exible leads32, 33 which are secured to the insulation plate 30 by means of a clamp34.

As already mentioned, the magnet yokes 16 are H- shaped. The legs 35, 36opposite to those on which the windings 24, 25 are disposed, serve assupports (FIG. 7). On a support bar 37 vertical bridges 38 are mountedwith regular spacing, against whose both flanks two respective magnetyokes 16 are located by means of their legs 35, 36. The magnet yoke legsare pressed against the bridges 38 by means of two tensioned and elasticU-clamps 39. A spring sleeve projecting from a hole 40 drilled throughthe support 37 serves as a stop for the tensioned clamps 39. Support 37has also holes 41 which serve for receiving a key 42, the shaft of whichhas an oval cross section (FIG. 8). By means of inserting key 42 in theholes 41, the clamps 39 can be opened by simply turning the keywhereupon the magnet yokes 16 can be released from their support.

This arrangement allows the easy and quick adjustment of the variousmagnets, which at the small tolerances normally necessary in suchprinting devices, always offers a problem of particular complexity: withthe winding 21 energized and the holding magnets 16 and armatures 15 inthe rest position, the support 37, in a manner which will be explainedhereinafter in this text, will be moved to bring the magnet yokes 16toward the magnetic armatures 15. Next, the clamps 39 are opened oneafter the other by inserting and turning the key 42, so that theindividual magnet yokes 16 are free to locate themselves independentlywith their armatures 15 under the inuence of the magnetic force of theholding winding 21 without any air gaps being formed. In order to avoida shafting of the mag-net yokes in a preferred direction upon theclosing of the clamps, hard A1203 crystals 44 are impregnated in thecontact faces of the bridges 38, the points of which are protruding fromthe surface embed themselves in the softer metal of the magnet yokes andthus prevent any sliding of the adjusted magnet yokes.

A restore bail 45 is provided to which is connected the support 37 andwhich is supported on leaf springs 49, 50 so as to be movable to bringthe magnets 16 into juxtaposition with their respective armatures 15.Movement of the restore bail 45 and consequently also of the magnetyokes 16 is effected through a drive which in FIGS. 2-5 is shown invarious positions. The restore bail 45 has a ledge 52. In the cavityformed thereby a roller lever 53 protrudes from below. On this leverroller 55 is supported by means of axle 54, said roller engaging withthe restore bail at the contact line 56. The restore bail is in turnpressed against the roller 55 by a helical spring 57 which is supportedby a stationary machine part 58. Roller lever 53 is supported on an axle59. On its other lever arm it carries a roller 60 which engages with acam disc 62 mounted on axle 61.

For receiving the motion energy of the print hammers moving back after aprint impact dampers 63 are provided for the individual print hammers,the damper mass of which corresponds approximately to the mass of theprint hammer (FIG. 9). The damper material 63, which iS secured to block65 through the layer of rubber 64, engages with the print hammers bymeans of locking levers 66 and consists of elastic material such as anylon composition, said levers being secured thereto at the lower edge.For that purpose the print hammers have upwardly projecting stops 67which push against the front side of the locking levers 66 duringbackward motion. For releasing the locking levers and for allowing thecontinued backward motion of the print hammers, the dampers are mountedpivotally, the locking levers 66 being pivoted out of the path of theprint hammer. The damper block 65 is for that purpose connected to arail 70 by means of screws 68, 69, said rail being in turn secured to anarm of a pivoted lever 71. The lever 71 is mounted on axle 72 (FIGS. 25). This axle is arranged in an offset or staggered position in adownward direction from the supporting point of locking lever 66, sothat upon upward motion of the locking lever there is little or nointerference between the print hammer and the locking lever. At theother arm of the pivoted lever 71 a roller 73 is supported for engagingwith a cam disc 74 which is also mounted on axle 61. Roller 73 isengaged with the disc 74 by means of springs 75.

Thus the operation motion is as follows. In the rest position the leafsprings 12, 13 are not tensioned and are in a relatively ilat position.The restore bail 45 is moved far enough to the front (to the right inFIGS. 2-5) that the magnet yokes 16 secured to it touch the armatures15. If the holding winding 21 on the magnet yoke 16 is energized, thearmatures 15 are held magnetically at the pole shoes of the magnetyokes. If now the shaft 61 starts its turning motion, lever 71 ispivoted by means of the cam disc 74 so that the locking lever 66 islifted upwardly out of the print hammer path. Under the influence of thecam disc 62 the restore bail 45 and support 37 are then moved back tothe left. The print hammers are carried along in the process and thesprings 12, 13 are thus tensioned. The damper mass 63 returns to itsoriginal position in the meantime. The locking levers 66 are now locatedwith a light spring tension against the sloping faces of the printhammer stops I67. If now a print hammer is released from the magnetyokes 1-6 by one of the compensating windings 24, receiving a pulse ofelectrical energy, it jerks forward, strikes the print type ag-ainst thepaper sheet and is stopped in its return motion by the damper lockinglever 66. The locking lever -66 is equipped with a weight 77 so as tomake sure that upon the effecting of a print impact, the damper isalready returned to the locking position. After all of the print hammershave been released for the line to be printed, the restore bail is movedforward again by the cam disc `62, so that the released print hammersmay be secured by their respective magnet yokes.

The leaf springs 12, 13 carrying the print hammers 11 are fixed withtheir lower ends secured in the foot platen 14 as already mentioned.Thus each print hammer forms a structural unit with its mounting and ifnecessary it can be removed and exchanged very easily. Two associatedfoot plates 14 are connected with each other by means of screws 78, 7 9,and 80 as shown in FIG. l, the guide plate `81 being interposedtherebetween. The guide plate 81 is located with its stop faces 82, 83,and 84 against the block 85 and the cover plate 86, and on the otherside it is inserted in slots yS7 of a plate 88. It is secured to theblock -85 by means of screw 89 and lock nut 90. The holes in the footplate 14 and the guide plate S1 for the screws '78, 79, and S0 aresufficiently large to provide clearance for the screws so that the printhammer units can be adjusted individually.

The securing of the leaf springs 12, 13 is effected at the top as wellas at the lower end in an elastic junction (FIGS. l0, 11). The slotsreceiving the ends of the leaf springs (slots 91, 92) are of increasedwidth in the upper portion. Besides that, they are enlarged towardstheir outer edges so as to form a cone-shaped funnel 93, 94. Therivet-shaped cavity formed in this manner is filled with an elasticsynthetic material 95 such as, for example, a nylon composition. At thetop ends of the leaf springs shoulders 496, 97 of the print hammers aresurrounded by the synthetic material 95 in order to extend the elasticjunction over the whole width of the leaf spring, which is wider thanthe width of the print hammer, the elastic material being tapered inthickness towards the midpoint of the springs. At their extreme ends 98,99, 100, and 101 the leaf springs are welded or otherwise suitablysecured to the print hammers and the foot plates, respectively.

In order to adjust for variations in the thickness of the leaf springs12, 13, spring U-bolts 102 are provided which are slidably movable alongthe leaf springs, said U-bolts fitting against the leaf springs at theirends with small rollers 103, 104 of synthetic material. The U-bolts arepositioned in grooves provided in opposite faces of, and are locked inthe foot plates 14, through the use of elastic locks 105, 106 positionedin the grooves 107, 108 and fitting against the bolts under pressure.These slidable U- bolts have the function of adjusting the action of thesprings 12, 13 to compensate for minor manufacturing tolerances in thethickness of the leaf springs, and permit a relatively ltine adjustmentof the hammer flight time.

Referring to the FIG. 12a, it will be seen that the holding winding 21which is common to all of the magnetic yokes 16 is connected to thepositive terminal of a 38 v. `source and to ground, through aninductance device L and a series resistor R. The bucking or neutralizingwindings 24 and 25 of the individual magnet yokes 16 are alsoconnected'to the same source through a resistor R1. The series resistorR1 is bridged by a capacitor C1 in order to effect a quick rise time ofthe magnetizing current. Again it is emphasized that the holding winding21 is common to all of the magnet yokes 16 whereas the bucking windings24 and 25 are individually arranged on each yoke and can be controlledindividually.

For that purpose, the other end of the series connected windings 24 and25 is connected to the collector of a transistor TR1 whose emitter isconnected to ground or zero potential. Normally the transistor TR1 isturned oli', but if a pulse is applied to its base by way of the ANDswitch A1 this transistor is turned on, and the bucking windings 24, 25are excited for a relatively short time.

The transistors TR for each of the print positions are controlled asfollows. The memory storage of the machine contains the text of a printline. By -comparison with an electronic image or representation of thecharacters on the type bar it is determined after each step of the typebar how many further steps of the type bar are required each time inorder to make sure that a type character corresponding to the characterto be printed in a particular position is located opposite this printingposition. If the number of steps required equals zero, that is, if acharacter to be printed lies opposite the particular printing positionin question, the corresponding AND switch A1 is prepared by raising theline x. When this has been carried out for all of the printing positionsfor a particular position of the type bar, a pulse is applied to raisethe line y of all AND switches A. Thus the transistors TR1 are turned onand the corresponding windings 24, 25 are energized, so that the printhammers are released, and a print impact is obtained in all 0f thoseprinting positions where the AND switches A have been prepared byraising the line x. By having the bucking windings 24 and 25 producing asufficiently strong magnetic lield, the magnetic field of the holdingwinding 21 is more than neutralized, and is overcompensated, therebyforcing collapse of the holding magnet iield more rapidly and areduction of the hammer flight time and a stabilization of the system isobtained.

In FIG. 12b the hammer flight time dependency on the ratio of the ampereturns of the bucking windings and of the holding winding, is shown. Thisshows clearly that the hammer flight time decreases with increasingvalues of a, and that between the values 1.6 and 2.0 it passes through avery liat minimum and that it subsequently rises again. The mostfavorable value of a is at approximately 1.76; considerable variationsin the values can occur, however, without there being any exceptionalchange in the hammer flight time, because of the flatness of the curvein this area.

The low influence of voltage variations can be seen by referring to FIG.12e where the lhammer flight time is plotted against relative variationsin the potential of the 38 v. source. In both FIGS. 12b and 12C thenormal variations are indicated by the hatched areas.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a print hammer unit for a high speed printer having movable meansfor presenting a plurality of type characters at a print line forcooperative print action by print hammer means,

a print hammer having a hammer portion adjacent the print line at eachof a plurality of print positions and having an armature portion,

resilient support means for each of said hammers including a pair ofparallel flat spring members,

means including electromagnetic means having a separate magnetic yoke ateach print position with a single hold winding common to all of theyokes operable to produce magnetic iiux in said armature portions tohold said armature portions away from the print line and flex saidspring members to store potential energy therein,

means operable to effect movement of said Ihammers in response to saidstored energy by reducing the flux in the armature portions below theholding point to effect release of said hammers.

2. In a print hammer unit, the combination in accordance with claim 1,characterized in that for the deactivation of the electromagnets holdingthe tensioned print hammers, individual release windings are arranged atthe various print positions on the magnet yokes in such a manner thatthe magnetic ield produced by them neutralizes the holding magnet eldand removes it from the armature, respectively.

3. In a print hammer unit, the combination in accordance with claim 2,characterized in that the magnetic field of the holding magnet isneutralized through the magnetic field of the releasing magnetindividual to the corresponding print position.

4. In a print hammer unit, the combination in accordance with claim 3,characterized in that the holding coil which is common to all magnetyokes and continuously carrying current is connected to a source ofelectrical energy in series with an inductance device of a high value.

5. In a print hammer unit, the combination in accordance with claim 4,characterized in that the magnet yokes near the pole faces have a crosssection which is reduced compared with th eremaining magnetic circuit,and that in this area they `are magnetized to the saturation point.

6. In a print hammer unit, the combination in accordance with claim 5,characterized in that the magnet yokes, preferably in pairs, are iixedon bridges mounted on a common carrier by means of tensioned clamps.

7. In a print hammer unit, the combination in accordance with claim 6,characterized in that the surfaces of the bridges, and the inside jawsof the tensioned clamps pressing the magnet yokes against the bridges,areimpregnated with hard crystals, preferably sintered A1203 (corundum).

8. In a print hammer unit, the combination in accordance with claim 7,characterized in that the magnet yokes are aligned individually towardstheir print hammers in such a manner that they automatically locatethemselves when the holding magnet is excited and clamps opened by meansof a key, and un-der the influence of the magnetic forces the tensionedclamps are held against the corresponding armature without an air gapbeing formed.

9. In a print hammer unit, the combination in accordance with claim 8,characterized in that carrier of the magnet yokes is supported on leafspr-ings and arranged in shiftable manner, and that cam means isprovided to actuate the carrier and provide a motion which goes back andforth periodically and which is also directed perpendicular to theplaten, said motion serving for the restoring of the red print hammers.

10. In a print hammer unit, the combination in accord* ance with claim9, characterized in that the print hammer units; preferably in pairs,are fixed in such a manner that they can be adjusted individually, asthey are secured to their foot plates iby stationary guide plates.

11. In a print hammer unit, the combination in accordance with claim 10,characterized in that the leaf springs carrying the print hammers aresurrounded at their top and lower ends with coatings ofelastic materialwhich fill cavities recessed in the print hammers and the foot plates,said cavities having the spring ends welded to their innermost ends, andthat these coatings taper continuously towards the middle of the spring.

12. In a print hammer unit, the combination in accordance with claim 11,characterized in that spring U-bolts are provided which are shiftablealong the leaf spring pairs carrying the print hammers, which furthertit with their end points against the leaf springs intermediate the endsthereof, and which are combined structurally through being slidablysupported in the foot plate of the corresponding print hammer unit, sothat these bolts serve for the adjustment of the hammer iiight time.

13. In a print hammer unit, the combination in accordance with claim 12,characterized in that at the individual print positions elasticallyfixed damper masses are provided which absorb the energy of the printhammers moving back after print impact, and which, by means of elasticlocks block the print hammers until the magnet yokes are moved to theirfront extreme positions to seize the print hammers.

14. In a print hammer unit, the combination in accordance with claim 13,characterized in that the damper masses are Iixed on a common carrierextending over all print positions, pivotally supported with its pivotpoint positioned below the elastic locks, said carrier being pivoted formovement for a short time for releasing the print hammers, preferably bymeans of a cam gear.

References Cited UNITED STATES PATENTS 2,940,385 6/ 1960 House lOl-933,049,990 8/1962 Brown et al. lOl- 93 3,144,821 v8/1964 Drejza lOl-933,156,180 11/1964 Barnes lOl-93 3,172,352 3/1965 Helms lOl-93 3,188,9466/ 1965 Schacht 101-93 3,209,682 10/ 1965 Cooper lOl- 93 3,266,4188/1966 Russo lOl-93 WILLIAM B. PENN, Primary Examiner.

1. IN A PRINT HAMMER UNIT FOR A HIGH SPEED PRINTER HAVING MOVABLE MEANSFOR PRESENTING A PLURALITY OF TYPE CHARACTERS AT A PRINT LINE FORCOOPERATIVE PRINT ACTION BY PRINT HAMMER MEANS, A PRINT HAMMER HAVING AHAMMER PORTION ADJACENT THE PRINT LINE AT EACH OF A PLURALITY OF PRINGPOSITIONS AND HAVING AN ARMATURE PORTION, RESILIENT SUPPORT MEANS FOREACH OF SAID HAMMERS INCLUDING A PAIR OF PARALLEL FLAT SPRING MEMBERS,MEANS INCLUDING ELCTROMAGNETIC MEANS HAVING A SEPARATE MAGNETIC YOKE ATEACH PRINT POSITION WITH A SINGLE HOLD WINDING COMMON TO ALL OF THEYOKES OPERABLE TO PRODUCE MAGNETIC FLUX IN SAID ARMATURE PORTIONS TOHOLD SAID ARMATURE PORTIONS AWAY FROM THE PRINT LINE AND FLEX SAIDSPRING MEMBERS TO STORE POTENTIAL ENERGY THEREIN, MEANS OPERABLE TOEFFECT MOVEMENT OF SAID HAMMERS IN RESPONSE TO SAID STORED ENERGY BYREDUCING THE FLUX IN THE ARMATURE PORTIONS BELOW THE HOLDING POINT TOEFFECT RELEASE OF SAID HAMMERS.